The present invention relates to improved elements for use in fuel cell stacks, and more particularly, to a stack having a corrosion resistant, electrically conductive, fluid impervious interface member therein.
It has been known for some time that fuel cells and stacks of such cells can be extremely advantageous as power supplies, particularly for certain applications such as a primary source of power in remote areas. It is highly desirable that any such fuel cell assembly be extremely reliable. Various fuel cell systems have been devised in the past to accomplish these purposes. Illustrative of such prior art fuel cells are those shown and described in U.S. Pat. Nos. 3,709,736, 3,453,149 and 4,175,165. A detailed analysis of fuel cell technology comparing a number of different types of fuel cells appears in the "Energy Technology Handbook" by Douglas M. Consadine, published in 1977 by McGraw Hill Book Company at pages 4-59 to 4-73.
U.S. Pat. No. 3,709,736, assigned to the assignee of the present invention, describes a fuel cell system which includes a stacked configuration comprising alternating fuel cell laminates and electrically and thermally conductive impervious cell plates. The laminates include fuel and oxygen electrodes on either side of an electrolyte comprising an immobilized acid. U.S. Pat. No. 3,453,149, assigned to the assignee of this invention, is illustrative of such as immobilized acid electrolyte. In U.S. Pat. No. 4,175,165, assigned to the assignee of the present invention, a stacked array of fuel cells is described wherein gas distribution plates include a plurality of gas flow channels or grooves with the grooves for the hydrogen gas distribution being arranged orthogonally relative to the grooves for the oxygen distribution. The gas distribution plates themselves, whether they are individual termination plates for one or the other of the gases, or bipolar plates for distributing both gases in accordance with this disclosure, are formed of an electrically conductive impervious material.
In larger stacks of fuel cells, heat dissipation from the cell's operation becomes a consideration. To solve this problem, cooling cells have been employed in the stack to maintain the thermal balance of stack. These cooling cells have frequently been made of a metal such as aluminum. Metal plates have also been utilized for the current collection element in fuel cell stacks. One problem which arises with respect to both the cooling plates and the current collecting plates in a fuel cell stack is that they are subject to corrosion attack by the acid electrolyte. In order to prevent corrosion, an interface layer has been utilized comprising a conductive carbon layer, such as Grafoil manufactured by Union Carbide Corporation, and a copper screen arranged between the cooling or current collecting plate and the next termination plate. The interface layer can be a highly rolled, densely-packed, carbon, fibrous material which is at least partially resistant to acid attack. Given the foregoing considerations in fuel cell stack designs, there is a continuing need to solve these problems while keeping the manufacturing and maintenance costs of the stacks as low as possible.
Accordingly, it is the aim of this invention to provide an improved interface configuration between elements of a fuel cell stack.
It is a further aim of this invention to provide such an interface configuration which is impervious to gas or liquids so as to impart resistance to corrosion by the electrolyte and to provide good electrical and thermal conductivity.
It is a further aim of this invention to provide a fuel cell stack including at least one of said improved interface configurations.
It is also an aim of this invention to provide a process for making the improved interface configuration and fuel cell stack as above.